redirect_stderr wasn't added to contextlib until Python 3.5

So it turns out that we need contextlib2 for Python 3.4 and earlier.

Author: tleonhardt

cmd2.py

@@ -73,6 +73,12 @@
 except ImportError:
     import subprocess
 
+# Python 3.4 and earlier require contextlib2 for temporarily redirecting stderr and stdout
+if sys.version_info < (3, 5):
+    from contextlib2 import redirect_stdout, redirect_stderr
+else:
+    from contextlib import redirect_stdout, redirect_stderr
+
 # Detect whether IPython is installed to determine if the built-in "ipy" command should be included
 ipython_available = True
 try:
@@ -92,12 +98,8 @@
 # BrokenPipeError is only in Python 3. Use IOError for Python 2.
 if six.PY3:
     BROKEN_PIPE_ERROR = BrokenPipeError
-
-    # redirect_stdout and redirect_stderr weren't added to contextlib until Python 3.4
-    from contextlib import redirect_stdout, redirect_stderr
 else:
     BROKEN_PIPE_ERROR = IOError
-    from contextlib2 import redirect_stdout, redirect_stderr
 
 # On some systems, pyperclip will import gtk for its clipboard functionality.
 # The following code is a workaround for gtk interfering with printing from a background

setup.py

@@ -67,9 +67,13 @@
 if sys.platform.startswith('win'):
     INSTALL_REQUIRES += ['pyreadline']
 
-# Python 2.7 also requires contextlib2 for temporarily redirecting stdout and stderr and subprocess32
+# Python 3.4 and earlier require contextlib2 for temporarily redirecting stderr and stdout
+if sys.version_info < (3, 5):
+    INSTALL_REQUIRES += ['contextlib2']
+
+# Python 2.7 also requires subprocess32
 if sys.version_info < (3, 0):
-    INSTALL_REQUIRES += ['contextlib2', 'subprocess32']
+    INSTALL_REQUIRES += ['subprocess32']
 
 # unittest.mock was added in Python 3.3.  mock is a backport of unittest.mock to all versions of Python
 TESTS_REQUIRE = ['mock', 'pytest']